The present invention relates generally to the field of signal transmission in radio telephony and remote functional or operational control of a radio device. More specifically, the present invention relates to an apparatus and method for facilitating time-critical frequency band selection within radiotelephone-based communication apparatus operable in more than one frequency band.
A conventional cellular network includes spaced-apart, fixed-site base stations. These base stations include transceivers for communicating with mobile stations (MS) or with hand-held phones (HHPs) which are physically present in the geographic area defined by the area covered or cell-site for each particular base station. Each HHP includes one or more transceivers for transmitting and receiving to/from the various or appropriate base stations. During conventional cellular telephone system operation, a mobile station (MS) or an HHP maintains contact with a primary base station when present within the specific geographic area or cell-site xe2x80x9ccoveredxe2x80x9d by that particular base station.
As used herein, the terms hand-held phone (HHP), mobile station (MS), and radiotelephone are used interchangeably. As is now well known in the art, traveling mobile stations traverse boundaries into xe2x80x9cnewxe2x80x9d geographic areas (i.e., a xe2x80x9cnewxe2x80x9d cell). Contact is maintained while traversing geographic areas by implementing communication between the MS and the xe2x80x9cnewxe2x80x9d base station (used for maintaining communication with the land based communication system) when the HHP moves into the xe2x80x9cnewxe2x80x9d cell or geographic area. This is often referred to as xe2x80x9chanding-offxe2x80x9d the phone from one base station to another. Handing-off oftentimes requires transfer to a channel comprising a different frequency within the frequency band because of the inherent construction of cellular systems.
FIG. 1 is a typical cell diagram defining a cellular configuration for a conventional cellular telephone network 100. Cellular network 100 operates in accordance with one of a number of known air interface types, including, for example, time division multiple access (TDMA) protocol. In a TDMA system, for example, each cell within the cellular network operates with an assigned set of transmit and receive frequencies selected from one or more of the available frequency bands. Presently, each set contains multiple paired transmit and/or receive frequencies, typically referred to as channels, and which operate on different frequencies for adjacent cells. The cellular network 100 as shown in FIG. 1 supports operation in both the cellular (approximately 800-900 MHz) band and personal communication service (PCS) band (approximately 1.9-2.0 GHz).
Cellular network 100 includes a base station (BS) 14(1)-(15) within each cell 12(1)-(15). The base stations 14 engage in simultaneous communications with a plurality of mobile stations (MS""s, radiotelephones, HHP""s, carphones, handsets, etc.) 16 operating roughly within the area of coverage associated with a particular cell 12. At least one control channel is assigned to each base station 14 and is used to carry system radio frequency (RF) control signals between the base stations 14 and the HHPs 16 operating within the base station""s area of coverage. These control channels also assist the network with mobile station cell re-selection. Mobile switching centers (MSC) 18 are connected with each other and connected with the public switched telephone network (PSTN) 20, and communicate using control signals and voice/data signals to selectively connect subscriber voice and data communications to the mobile stations 16 through the base stations 14. MSC""s are also used in handing-off subscriber communications from a traffic channel of one cell 12 to a traffic channel of another cell as the mobile station 16 roams throughout the cellular service areas (i.e., the network).
For example and referring to FIG. 1, MS 16(1) may be a cellular only device which is traveling through areas covered by base stations 14(2), 14(7), 14(12), and 14(15) on a path from A-to-a. MS 16(1) will communicate with cellular band base station 14(2) while in its area of coverage 12(2). MS 16(1) will be handed off to cellular/PSC band base station 14(7) which will communicate with MS 16(1) in the cellular band since MS 16(1) does not have the capability to communicate on the PCS band. In a similar manner, MS 16(1) will be handed off to cellular band base stations 14(12) and 14(15) when the MS is in their areas of coverage.
MS 16(2) may, for example, be a PCS only device which is traveling through areas covered by base stations 14(1), 14(5), and 14(10), and not communicate with BS 14(14) while on a path from B-to-b. MS 16(2) will communicate with cellular/PCS band base station 14(1) while in its area of coverage 12(1) using the PCS band only. When MS 16(2) moves into the area of coverage 12(5) of base station 14(5), then the MS will be handed off to BS 12(5). In a similar manner, MS 16(2) will be handed off to cellular/PCS band base stations 14(10). However, when MS 16(2) reaches the area of coverage 12(14) of base station 14(14), cellular only base station 14(14) will not be able to provide service, and MS 16(2) will attempt to find service by roaming. When no PCS capable base station is available, this MS 16(2) will typically report xe2x80x9cNo Servicexe2x80x9d.
Where, for example, MS 16(3) is a dual band device, (e.g., cellular and PCS), then in a similar manner as MS 16(1) and MS 16(2), as MS 16(3) travels on a path from C-to-c, the phone may operate in the cellular band while in the area of coverage 12(13) of base station 14(13), and in either the cellular band or the PCS band when it is in the areas of coverage 12(10), 12(7), and 12(4). In a similar manner, where MS 16(4) is also a dual band device, it may operate in cellular band while in the area of coverage 12(3) of base station 14(3) and may operate in PCS band while in the areas of coverage 12(5) and 12(7) of base stations 14(5) and 14(7). However, as MS 16(4) leaves the area of coverage 12(7), it will have to operate in the cellular band to maintain communications with base station 14(9). Dual MS 16(5), however, would not be required to switch between the cellular band and the PCS band while traveling on a path from E-to-e. In the PCS (only) band mode, MS 16(5) can communicate with base stations 14(1), 14(5), 14(7) and 14(4), while traveling from E-to-e. In the cellular (only) band mode, MS 16(5) can communicate with base stations 14(1) or 14(3), 14(5) or 14(1), 14(2) or 14(5), 14(2) or 14(7), 14(7) or 14(4), and perhaps 14(9) while traveling from E-to-e.
Where MS 16(1), 16(3), 16(4), and 16(5) are present simultaneously in an area of coverage 12(7) such as that controlled by base station 14(7), then it is advantageous to operate certain MS devices in one band while operating other of the MS devices in the other band.
Traditionally, mobile radiotelephones were constructed to operate in either the cellular band or the more recently allocated PCS band networks. For example, hand-held phones were constructed exclusively for a wireline/non-wireline network (cellular band) or PCS network (PCS band). FIG. 2a shows a block diagram of a conventional radio communication (hand held phone) device 200 including a transceiver (FIG. 3 of U.S. Pat. No. 5,430,416, issued Jul. 4, 1995, to Black, and the patent incorporated herein by reference). Device 200 provides the ability for a mobile station (or HHP) to communicate with a base station. In such a device or HHP, communication is carried out, for example, over various radio frequency (RF) channels. Upon receipt of an RF signal transmitted by an HHP present in a cell""s geographic area, the base station thereafter typically maintains communication signals with a land-line telephone system (not shown) and/or other HHP""s or mobile stations present in the cell area or geographic area.
The mobile station device 200 of FIG. 2a includes an antenna 201, a duplexor 202, a receiver 203, a transmitter 205, a reference frequency signal source 207, a phase locked loop (PLL) frequency synthesizer 208, a processor 210, an information source 206 and an information sink 204. When an RF signal 220 is received at antenna 201 from a base station, it is first filtered by the duplexor 202 to separate the RF received signal at line 211 from any RF transmit signals which may also be present at line 213, using a switch or filter contained therein (not shown in FIG. 2a). The receiver 203 is connected to receive the RF input signal via line 211 and is operative to produce a received baseband signal for transfer via line 212 to information sink 204. Reference frequency signal source 207 provides a reference frequency signal via line 215 to PLL frequency synthesizer 208. The frequency synthesizer also receives information from data bus 218, and operates in response to the data bus data to synthesize transmitter and receiver reference signals and to provide the those signals over lines 216 and/or 217 for use by either receiver 203 and/or transmitter 205.
Processor 210 controls operation of the PLL frequency synthesizer 208, receiver 203 and transmitter 205 via the data bus 218. The information source 206 produces a baseband amplitude modulation (AM) signal and provides it via line 214, as well as a baseband phase modulation (PM) signal via line 221. As mentioned, the transmitter utilizes the source information and the carrier signal to generate an RF transmit signal for transfer to duplexor 202 via line 213. The duplexor connects the RF transmit signal for emission by antenna 201, the transmitted signal referred to hereinafter as RF output signal 220.
As radiotelephone technology has evolved, it has become desirable to include transceivers within hand-held phones which can operate in both the cellular and PCS bands. This is particularly helpful where HHPs operate in areas which allow communication via two (and perhaps more) bands. Such a cellular telecommunication network is disclosed in U.S. Pat. No. 5,761,623, incorporated herein by reference. One complication in such a network, though, is that band-specific components need to be timely switched when necessary to minimize transmission errors and/or requests for retransmission either to or from the HHPs.
Shown in FIG. 2b is another prior art communication device 99. Device 99 includes an antenna 110, a duplexer 120 (or optional triplexer 124), a low noise amplifier (LNA) 124, receive circuitry 125, transmit circuitry 126, a power amplifier (PA) 129, an optional extra band power amplifier 130, a microcontroller 150, a CODEC 160, a speaker 160, and a microphone 180. For dual band operation, duplexor 120 is replaced by triplexer 124, and typically a second PA is used to provide an amplified signal to triplexer 124, as is well known in the art.
Conventional xe2x80x9cinxe2x80x9d (or intra) band switching is often implemented due to a frequency change request received by the HHP""s controller, thereafter affecting the frequency synthesizer and the HHP""s transceiver""s operation. For band to band (inter) switching, such conventional (intra) band-switching operations can often times be untimely due to the fact that band-specific circuitry is activated only after the frequency change and/or band change information is decoded by the controller. The conventional band to band switching operations may not be timely or may need to be made more time efficient for certain band to band switching operations. For example, each band of a network employing more than one band may require specific physical elements or components such as filters, amplifiers, oscillators, etc. (typically referred to hereinafter as band-specific circuitry), which are for use by the HHP when operating within one particular band. The band-specific circuitry may only be activated or enabled as needed, and typically may require an enablement time from a xe2x80x98not in usexe2x80x99 condition or state to an xe2x80x98in usexe2x80x99 operational condition or state before such circuitry can be reliably or appropriately used.
Presently, it is well known that intra band operating frequency transitions typically occur while the HHP is in communication with one or more base stations. Further, band to band transitions may occur where the HHP is implementing an operational switch or transfer from a first base station to another base station. These band to band transitions may also occur if the HHP has been requested to report various signal strength measurements of another base station""s signals as part of the base station to base station transfer or handoff process. Presently, these handoff processes wherein the HHP reports these signal strengths are referred to as Mobile Assisted Hand-Off""s (MAHO""s). The band to band transitions are likely to occur if the xe2x80x9cnewxe2x80x9d base station has dual cellular and PCS mode capability, and one of the operating bands of the xe2x80x9cnewxe2x80x9d base station is over utilized.
Such band-switching operations have been implemented for one or more of a variety of reasons, such as: 1) implementing an actual first band channel to second band channel hand-off; 2) to enable the HHP to conduct mobile assisted hand-off (MAHO) measurements during conversation mode; or 3) to scan or receive data about a plurality of neighboring base stations, each operating in differing bands, such as cellular and PCS. It should be observed that before the synthesizer can tune to the proper xe2x80x9cin-bandxe2x80x9d frequency, the appropriate band circuitry or components must be effected so that the proper transmission channel is capable of being received from the RF signals. Because band switching is typically a time critical task, an increase in a HHP""s ability to timely switch to or between different bands in a system such as TDMA concomitantly increases the network""s overall performance.
Therefore it is desirous to implement a transceiver capable of operating within a device or communication system which has an ability to facilitate time-critical and/or more efficient band switching within the transceiver""s circuitry or other band specific components. Likewise, such circuitry would be useful as transmitting and receiving circuits of other communication equipment. As an example, it would be useful to implement such a methodology or apparatus in an HHP capable of a first band to second band followed by a second band to the first band switching operation in a more time efficient manner. These band switching and other operations could then preferably be performed during certain periods wherein the network was not intensively communicating with the HHP, thereby permitting additional operations or services to be accessed by the HHP, perhaps without apparent interruption of service to the HHP user. Further, such a methodology or apparatus may become preferred as the operating costs in one particular band may be less or limited with respect to another. It would therefore make it more desirable and cost efficient to operate or receive certain services in a particular band of a system employing two or more bands, provided the HHP is capable of seamlessly switching between the various bands of operation. Further, certain of these services may only be available in one band and not available in other bands. Thus, an ability to timely, efficiently, or seamlessly switch between different bands would effectively render such services available to the HHP and the HHP user, potentially without apparent disabling of the other services provided to the HHP.
It is therefore an object of this invention to provide both a circuit and method for implementing automated band selection which facilitates certain time critical switching operations.
It is another object of this invention to provide both a circuit and method for implementing automated band selection which facilitates efficient band to band switching operations.
It is another object of the invention to provide a transceiver system including reception and transmission circuitry and a method for operating the circuitry which implements automated band selection with improved enabling timing for switching band-specific components or circuitry used within an HHP during critically timed band to band operations, e.g., mobile assisted hand off (MAHO) where the HHP receives a band measurement order for another band.
It is another object of the invention to provide circuitry and a cost effective method for implementing band selection within transceivers which heretofore have not incorporated dual or multiband capability due to cost constraints, thereby providing a cost reduced HHP which is capable of efficient dual band or multiband switching.
It is another object of the invention to provide a system, circuit and/or method for implementing automated band selection with improved band to band switching characteristics of transceivers used in communication systems such as TDMA, CDMA, PHS, PCD or GSM and various other communication systems which implement a transceiver and which must make time critical changes between two operating frequencies wherein the frequencies are located much farther apart than the frequencies of which a conventional frequency synthesizer normally switches between.
It is also an object of the invention to provide a method for selecting a mode of operation of the transceiver such that certain functions or operations within the transceiver are implemented by accessing the incoming data stream to determine at least a portion of an immediate functional or operational state of the transceiver and to direct or control the transceiver accordingly.
The instant invention as related to the preferred embodiment disclosed herein incorporates a method for automated band selection for use in the receive chain architecture of an HHP or like communication apparatus to facilitate time-critical band to band switching. That is, while the communication apparatus is implementing a change of frequency command which may or may not require a band change, it is first determined whether the frequency in use should be switched to a frequency in a different band or frequency set. This permits faster selection or enabling of band-specific circuitry, if needed. This method can also be implemented by preevaluating the frequency command signal by using a microcontroller or digital signal processor (DSP), or both, programmed with an appropriate set of computer instructions or interrupt commands implementing the inventive concepts described herein. The preferred embodiment disclosed herein utilizes a latching circuit to extract or capture a band functional bit or control (or xe2x80x9cextraxe2x80x9d) bit used to identify or select the appropriate band of operation.
Additionally, the invention may employ one or more latch and/or logic circuits in combination which provide one or more operation control signals to the transceiver when implementing a frequency change from a current operating frequency to another frequency or channel in another band. The latch circuit captures one or more bits in the frequency change data bit stream and in combination with the logic circuit generates one or more switching signals therefrom. This automatically enables bandspecific circuitry to be selected for use with the frequency synthesizer during operation in the new band. The latching and/or logic circuit(s) may be implemented by discrete logic elements, as components of an ASIC, or by any other circuitry or combination of circuitry typically relied upon by those skilled in the art of generating and directing high speed signals typically used for enabling or controlling other circuitry.
Further, the functional bit or perhaps up to a plurality of functional bits within the data bit stream can be used for implementing other time critical functions or other less efficient control functions of the transceiver in addition to, or in supplementation to, or in replacement of the band to band switching as described herein. In short, the inventive concepts described herein are not limited to the disclosed band to band switching, but can be implemented for various other operational functions or states of a transceiver or HHP, particularly those functions, operations, or states that are time critical.
Whether implemented by hardware or by software utilized in a controller or DSP or a combination thereof, the functional operation of the invention utilizes a functional bit or xe2x80x9cextraxe2x80x9d bit included with a data stream or data word which is at least implicitly included within the command data received by the transceiver. The controller is used to evaluate a future operating condition or state of the transceiver and subsequently provides the data stream or data word and/or control signals to circuitry within the transceiver thereby effectuating activation of circuitry used for achieving the condition or state.
The software controlled microprocessor, DSP, and/or the latch circuits receive the command data and extract a frequency data word which is then provided to tune the frequency synthesizer. A functional bit or xe2x80x9cextraxe2x80x9d bit is concurrently extracted or captured to generate a band select signal which is provided to activate the appropriate band specific circuitry. In the preferred embodiment, the xe2x80x9cextraxe2x80x9d bit is specifically extracted to form a control signal used to activate the appropriate band-specific elements and circuitry within the receive and transmit chain signal paths. For example, the control signal may control, activate, or effect cellular specific circuits or PCS specific circuits, one set of which were previously in an xe2x80x9coffxe2x80x9d state before receipt and determination of the switch to a new band command.
Additionally, the invention overcomes the lack within TDMA chipsets of a provision to generate a band switch signal capable of controlling such a time-critical event. That is, conventional TDMA chipsets control the timing of the synthesizer data but provide no ability for time critical PCS/Cellular band switching. The band switching logic disclosed herein may supplement or be included in conventional TDMA chipsets or other chipsets used for controlling HHP""s. The inventive concepts may be implemented by software capable of controlling an output node of the chipset depending on the anticipated state of the band.
It should also be noted that any number of bits may be inserted into the frequency command signal or the frequency data word to logically identify which of a plurality of bands the xe2x80x9cnewxe2x80x9d frequency will reside, and to likewise automatically enable circuitry specific to the xe2x80x9cnewxe2x80x9d band. Hence, circuits which support operation in one band of a dual band apparatus, or a single band in a multi-band apparatus, are enabled in response to the band bit(s) while the frequency data word is decoded by the controller for subsequent use by the frequency synthesizing circuitry. It is important to note that including and extracting one or more xe2x80x9cextraxe2x80x9d bits in/from the frequency command data does not disturb the frequency data word. Such operation is possible because these xe2x80x9cextraxe2x80x9d bits are bits which are typically rolled off the end of a shift register buffer in which the bits of the command signal are momentarily stored prior to being captured or locked by a data word locking signal, e.g., a latching signal or a data lock strobe signal. The timing of the data word locking signal actually controls the latching of the data of the frequency data word.